Host-sensitized
phosphorescence
of
Mn
4+
,
Pr
3+,4+
and
Nd
3+
in
MgAl
2
Si
2
O
8
Esra
C¸ırc¸ır
a,
Nilgun
Ozpozan
Kalaycioglu
b,*
aDepartmentofMaterialsScienceandEngineering,FacultyofEngineering,Karamanog˘lu MehmetbeyUniversity,Karaman,70200,Turkey bDepartmentofChemistry,FacultyofScience,ErciyesUniversity,Kayseri38039,Turkey
1. Introduction
Luminescentmaterialswithlongafterglowarekindsofenergy storagematerialsthatcanabsorbbothUVandvisiblelightfrom thesunandgraduallyreleasethisenergyinthedarkatacertain wavelength. These kinds of long lasting phosphors have been widelystudiedbymanyresearchers[1–3].
Silicatesthereforearesuitablehostsforphosphorsbecauseof theirhighphysicalandchemicalstability.Theluminescenceofrare earthionsinthesilicatehosthasbeenstudiedforalongtime.In recentyears,silicatephosphorshavebeenreportedbyresearchers [4–13].
In this paper, MgAl2Si2O8:Mn4+,Pr3+,4+ and MgAl2Si2O8: Mn4+,Nd3+ based phosphors were synthesized 13008C. Their thermalbehavior,crystalstructure,morphologicalcharacterization, photoluminescencepropertiesandexcitationmechanismwerethen investigated.
2. Experimental
MgAl2Si2O8:Mn4+,Pr3+,4+ and MgAl2Si2O8:Mn4+,Nd3+ phos-phors were synthesized at 13008C. All the starting materials, 4MgCO3Mg(OH)25H2O (A.R.), Al2O3 (99.0%), SiO2 (99.8%), MnO2 (99.0%), Pr6O11 (99.99%) and Nd2O3 (99.99%) were weighed according to the nominal compositions of (Mg0.84Mn0.10Pr0.06)Al2Si2O8 and (Mg0.88Mn0.10Nd0.02)Al2Si2O8.
Thesepowdersweremixedhomogeneouslyinanagatemortar for 3h.Smallquantitiesof H3BO3 (A.R.) wereaddedas a flux duringthemixing.Asmallamountofeachsamplewastakenfor thermalanalysis(DTA/TG)tostudythephase-formingprocess. Thermogravimetry(TG)anddifferentialthermalanalysis(DTA) were carried out by using a DTA/TG system (Perkin Elmer Diamondtype).Thesampleswereheatedatarateof108Cmin1 fromroomtemperatureto13008C,inthenitrogenatmosphere. Afterwards,thesinteringconditionsofthephosphors,including the pre-firing temperature and synthesizing temperature, were determined intotwo steps: first, the mixtures werepre-fired at 9008Cfor3hinaporcelaincrucibleinair,andthenthepre-fired samplesweresinteredat13008Cfor3hinair,inaporcelaincrucible. Aftertheseproceduresthephosphorswereobtainedandtheircrystal structureswereexaminedbyX-raydiffraction(XRD)analysisusinga BrukerAXSD8Advancediffractometerwhichwasrunat20–60kV and6–80mA,2
u
=10–908andastepof0.0028usingCuKa
X-ray. Scanningelectronmicroscopy(SEM)imagesandEDXanalysis wereperformedonaLEO440modelscanningelectronmicroscope usinganacceleratingvoltageof20kV.The decay time, excitation and emission spectra of the phosphors were recorded by a Perkin Elmer LS 45 model luminescencespectrophotometerwithxenonlamp.
3. Resultsanddiscussion
3.1. Thermalbehavior,crystallizationandmorphology
Fig.1illustratestheDTA/TGcurvesofnominalcompositionfor MgAl2Si2O8: Mn4+,Pr3+,4+. The curves below 2008C include the
MaterialsResearchBulletin47(2012)1138–1141
ARTICLE INFO
Articlehistory:
Received31October2011
Receivedinrevisedform21November2011 Accepted8February2012
Availableonline16February2012
Keywords: Mn4+ Pr3+,4+ Nd3+ MgAl2Si2O8phosphors Aluminosilicates ABSTRACT
Mn4+dopedandPr3+,4+,Nd3+co-dopedMgAl
2Si2O8-basedphosphorswerefirstofallsynthesizedabout
13008C.Theywerecharacterizedbythermogravimetry(TG),differentialthermalanalysis(DTA),X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The luminescencemechanismofthephosphors,whichshowedbroadredemissionbandsintherangeof610– 715nmandhadadifferentmaximumintensitywhenactivatedbyUVillumination,wasdiscussed.Sucha redemissioncanbeattributedtotheintrinsicd–dtransitionsofMn4+.
ß2012ElsevierLtd.Allrightsreserved.
*Correspondingauthor.Tel.:+905056441170;fax:+903524374933. E-mailaddress:nozpozan@erciyes.edu.tr(N.OzpozanKalaycioglu).
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dehydrationof4MgCO3Mg(OH)25H2Oandthedecompositionof H3BO3whichchangesintoB2O3.Thefirstendothermicpeakis(at 2408C,pointA)attributedtothedeviationofthehydroxylgroup fromMg(OH)2.Thesecondendothermicpeak shows(at 4378C, pointB)thedecompositionofMgCO3whichchangesintoMgO.
FromtheaboveDTA/TGanalysis,wecarriedoutthesinteringof thephosphorsintwosteps:first,thesampleswerepre-firedat 9008C for 3h to achieve the dehydration and decomposition ofH3BO3,MgCO3andMg(OH)2,andtohelpthedopedMn4+and
rare-earthionstosubstitute;nextthephosphorswereprepared at 13008C for 3h in air. Actually, the crystal systems were not observed at 9008C, but at 13008C for 3h the (Mg0.84Mn0.10Pr0.06)Al2Si2O8 and (Mg0.88Mn0.10Nd0.02)Al2Si2O8 tricliniccrystalsystemswereobserved(Fig.2).
TheXRDpatternsofphosphorsobtainedat9008Cand13008C for3hinairareshowninFig.2(a)and(b).Theunitcellparameters ofphosphorcrystallizedinthetriclinicsystemarelistedinTable1. Figs.3and4showtheimagesandEDXanalysisobtainedfrom thescanningelectronmicroscopy(SEM)ofthephosphorscalcined at13008Cfor3h.Themicrostructuresofthephosphorconsistedof regularfinegrainswithanaveragesizeofabout0.5–2.5
m
m. 3.2. PhotoluminescencepropertiesFig. 5 shows the excitation and emission spectra of the MgAl2Si2O8:Mn4+,Pr3+,4+ phosphor annealed at 13008C. The excitation spectrum of the MgAl2Si2O8:Mn4+,Pr3+,4+ phosphor observedwithMn4+emissionsat662nm(d–dtransitions)consists ofanexcitationbandwithamaximumat258nm.Under258nm UV excitation, the MgAl2Si2O8:Mn4+,Pr3+,4+ phosphor shows a strong red luminescence ranging from 600 to 750nm with a maximum;at662nmandsomelines(611,634,and710nm)inthe longerwavelengthregion.Theredemissionat662nm,whichcan be viewed as a typical Mn4+ emission, was ascribed to d–d transitions[14].Theemissionbandsat611nmand634nmaredue to the transitions of Pr3+ (1D
2!3H4) and Pr4+ (1D2!3P0), respectively[15].Inordertoidentifytheoriginoftheemission band of the MgAl2Si2O8:Mn4+,Pr3+,4+ phosphor at 710nm, we compared the emission spectrum of the undoped MgAl2Si2O8 sample under the same excitation conditions (258nm). We
Fig.1.TG/DTAcurvesofMgAl2Si2O8:Mn4+,Pr3+,4+phosphor.
Fig.2.XRDpatternsof(a)(Mg0.84Mn0.10Pr0.06)Al2Si2O8,(b)(Mg0.88Mn0.10Nd0.02)Al2Si2O8.
Fig.3.SEMimageof(a)(Mg0.84Mn0.10Pr0.06)Al2Si2O8,(b)(Mg0.88Mn0.10Nd0.02)Al2Si2O8phosphors.
reported the spectrum of the undoped MgAl2Si2O8 in the our previousarticle[16].Itshowedanemissionrangingfrom600to 800nmwiththethreemaximumat617,710and720nm(Fig.6). The broad MgAl2Si2O8 emission band can be attributed to the recombinationofanelectronandadonor.Therecombinationwas caused by crystal defects which occurred in the undoped MgAl2Si2O8duringtheprocess.Theemissionbandat710nmin theMgAl2Si2O8:Mn4+,Pr3+,4+phosphorhasthesameprofileasthat oftheundopedMgAl2Si2O8(Fig.6);thus,itcanbeascribedtothe hostemission.
The excitation and emission spectra of the MgAl 2-Si2O8:Mn4+,Nd3+phosphor areshowninFig.7.Underexcitation at258nm,theMgAl2Si2O8:Mn4+,Nd3+phosphorexhibitsastrong red luminescence. The excitation spectrum of the MgAl 2-Si2O8:Mn4+,Nd3+phosphor(Fig.7)observedwithMn4+emission at675nm(d–dtransitions)showsastrongexcitationbandwith
maximum at 258nm. When the phosphor was excitated at 258nm, only one emission peak located around 675nm was observedontheemissionspectrum.Suchabroadredemissionat 675nmcanbeviewedasthetypicalemissionofd-dtransitionsof Mn4+.TypicalemissionpeaksofNd3+werenot observedinthe emissionspectrumoftheMgAl2Si2O8:Mn4+,Nd3+phosphor.
Whenconsideringtheexcitationmechanism,inFigs.5–7,there isonly onepossibleexplanationfor theexcitation bandsofthe MgAl2Si2O8:Mn4+,Pr3+,4+ and MgAl2Si2O8:Mn4+,Nd3+ phosphors: thisishostcrystalabsorption.Theexcitationspectraofthehost MgAl2Si2O8(Fig.6)areinagreementwiththeexcitationspectraof the MgAl2Si2O8:Mn4+,Pr3+,4+ (Fig. 5) and MgAl2Si2O8:Mn4+,Nd3+ (Fig.7)phosphors.Thisindicatesthatalloftheexcitationbandof the MgAl2Si2O8:Mn4+,Pr3+,4+ and MgAl2Si2O8:Mn4+,Nd3+ phos-phorsat258nmarisefromhostlatticeabsorption.Theexcitation energyat258nmisfirstcapturedandthentransferredtotheMn4+
Table1
Unitcellparametersofphosphors.
Phosphor a(pm) b(pm) c(pm) V(106
pm3
) a(8) b(8) g(8) (Mg0.84Mn0.10Pr0.06)Al2Si2O8 598.27 1074.64 1480.16 737.70 83.84 79.79 125.31
(Mg0.88Mn0.10Nd0.02)Al2Si2O8 554.01 1123.27 1536.98 641.96 53.20 63.65 58.70
Fig.4.EDXanalysisof(a)(Mg0.84Mn0.10Pr0.06)Al2Si2O8,(b)(Mg0.88Mn0.10Nd0.02)Al2Si2O8phosphors.
Fig. 5. The excitation and emission spectra of (Mg0.86Mn0.10Pr0.06)Al2Si2O8
phosphor. Fig.6.TheexcitationandemissionspectraofMgAl2Si2O8phosphor.
E.C¸ırc¸ır,N.OzpozanKalaycioglu/MaterialsResearchBulletin47(2012)1138–1141 1140
andPr3+,4+ionsbythehostcrystal.ThepresenceoftheMgAl 2Si2O8 host crystal’s excitation band in the excitation spectra of MgAl2Si2O8:Mn4+,Pr3+,4+ and MgAl2Si2O8:Mn4+,Nd3+ phosphors showsthat anenergytransfertakes placefromtheMgAl2Si2O8 hostcrystaltotheMn4+andPr3+,4+ions.Theexcitationenergyof thehostcrystalMgAl2Si2O8dopedwithMn4+andPr3+,4+ionscan benonradiativelytransferredtoMn4+andPr3+,4+ions.Asshownin Fig.7 theenergy transferfromtheMgAl2Si2O8 to Mn4+ionsis complete.However,Fig.5showsthattheemissionbandat710nm from the MgAl2Si2O8 host lattice can still be observed in the emissionspectrumMgAl2Si2O8:Mn4+,Pr3+,4+.Thereforetheenergy transferfromtheMgAl2Si2O8hostcrystaltotheMn4+ionsisnot
complete.In addition,thereis noenergytransferfromthehost crystalMgAl2Si2O8totheNd3+ions.
TheluminescencedecaycurveoftheMgAl2Si2O8:Mn4+,Pr3+,4+ phosphor isshowninFig.8.Decaytimecanbecalculatedbya curvefitting methodbasedon thefollowing singleexponential equation:
I¼A1exp t
t
1þC
whereIisphosphorescenceintensity;A1,Careconstants;tistime; and
t
1isthelifetimefortheexponentialcomponents.Decaytime (t
1)forexponentialcomponentofMgAl2Si2O8:Mn4+,Pr3+,4+ phos-phorwas9.12ms.TheMgAl2Si2O8:Mn4+,Pr3+,4+phosphor shows muchlonger afterglowthan theundopedMgAl2Si2O8 phosphor whichindicatesthatMn4+,andPr3+,4+ionsplayanimportantrole inprolongingtheafterglow.ThedecaytimeoftheMgAl2Si2O8:Mn4+,Nd3+phosphorcannot bedetectedandcalculatedinthesameconditions.
4. Conclusion
In this report, (Mg0.84Mn0.10Pr0.06)Al2Si2O8 and (Mg0.88Mn0.10Nd0.02)Al2Si2O8 redphosphors werefirst prepared at13008Cfor 3h.Thephosphorshada tricliniccrystalsystem. Under UV excitation at 258nm, MgAl2Si2O8:Mn4+,Pr3+,4+ and MgAl2Si2O8:Mn4+,Nd3+ phosphors showed strong red lumines-cence. Themechanism of excitationin MgAl2Si2O8-based phos-phorswasexplainedbyanenergytransferfromtheMgAl2Si2O8 hostcrystaltotheMn4+andPr3+,4+ions.
Acknowledgement
ThisworkwassupportedbyErciyesUniversityEUBAPunder ProjectNo.FBD-09-804.
References
[1]Y.Lin,Z.Tang,Z.Zhang,C.Nan,J.AlloysCompd.348(2003)76.
[2]Y.Wang,Z.Wang,P.Zhang,Z.Hong,X.Fan,G.Qian,Mater.Lett.5(2004)3308. [3]C.K.Chang,D.L.Mao,ThinSolidFilms460(2004)48.
[4]G.Blasse,W.L.Wanmaker,J.W.terVrugt,A.Bril,PhilipsRes.Rep.23(1968)189. [5]T.L.Barry,J.Electrochem.Soc.115(1968)733.
[6]T.L.Barry,J.Electrochem.Soc.115(1968)1181. [7]P.B.Moore,T.Araki,Am.Miner.57(1972)1355.
[8]K.Yamazaki,H.Nakabayashi,Y.Kotera,A.Ueno,J.Electrochem.Soc.133(1986) 657.
[9]S.H.M.Poort,H.M.Reijnhoudt,G.Blasse,J.AlloysCompd.241(1996)75. [10]L.Huang,X.Zhang,X.Liu,J.AlloysCompd.305(2000)14.
[11]S.Ye,Z.Liu,X.Wang,J.Wang,L.Wang,X.Jing,J.Lumin.129(2009)50. [12]F.Clabau,A.Garcia,P.Bonville,D.Ganbeau,T.Mercier,P.Deniard,etal. J.Solid
StateChem.181(2008)1456.
[13]Y.Ding,Y.Zhang,Z.Wang,W.Li,D.Mao,H.Han,J.Lumin.129(2009)294. [14]T.Murataa,T.Tanoueb,M.Iwasakib,K.Morinagaa,T.Hasec,J.Lumin.114(2005)
207–212.
[15]D.Jia,Chem.Phys.Lett.363(2002)241–244.
[16]N.OzpozanKalaycioglu,E.C¸ırc¸ır,J.AlloysCompd.510(2012)6–10. Fig. 7. The excitation and emission spectra of (Mg0.88Mn0.10Nd0.02)Al2Si2O8
phosphor.
Fig.8.Thedecaycurvesofthe(Mg0.84Mn0.10Pr0.06)Al2Si2O8phosphor.
